Swine, poultry and other livestock are commonly reared in facilities that are specially designed to manage manure and liquid waste generated by such livestock. For example, poultry are typically raised on beds of litter that contain a filler such as wood shavings or saw dust, spilled food, feathers, and manure. After a growout on the bed of litter, and during successive growouts, the litter is predominantly manure, and is eventually replaced by fresh bedding.
Some swine rearing facilities have slatted floors on which the swine are raised. Beneath the floors are pits for receiving swine manure and urine that pass through the slatted floor. These pits contain water that is occasionally drained to remove the livestock waste. Other facilities raise swine on a hard slanted floor, and periodically wash accumulated manure and urine from the slanted floor. Still other facilities use a combined approach, and have slatted floors on which the swine are raised, and a slanted floor underneath that is periodically washed to remove accumulated manure and urine. Water that is used to flush manure in these facilities is often pumped into large tanks that can be quickly discharged to rapidly flush manure from the facility.
Dairy cows are also often raised in facilities that must periodically be washed of animal manure and urine. The dairy cows are often fed in a sheltered pen that has a hard concrete floor that is periodically washed.
Farmers manage the manure and waste water from livestock rearing facilities in several manners. Almost all farmers attempt to apply the manure and waste water onto agricultural fields. Some farmers spread the manure and waste water from the facilities directly onto their fields. When managing waste water, some farmers first send the waste water to a holding pond or lagoon before spreading the waste water onto their fields. Because solids tend to separate from the water in the center of the holding pond or lagoon, some farmers withdraw water from the center of the pond or lagoon and reuse it in their facilities to wash away excess manure.
Manure excreted by the poultry and other livestock generate ammonia that contributes to the offensive odor in many rearing facilities. Ammonia volatilization is especially acute in poultry facilities during the winter, when ventilation must be minimized to reduce heating costs. Ammonia volatilization is also acute in facilities that are flushed with recycled water from an anaerobic lagoon or holding pond. Nitrogen in swine lagoon effluent is mostly in the form of NH4, with little NO3 present. Indeed, ammonia concentrations of 350 mg/l and greater are common in lagoon effluent. In addition, because swine lagoon effluent is typically alkaline (pH>7.0), ammonia is favored over ammonium, resulting in conditions favorable for ammonia volatilization. When high pH water from swine lagoons is used for flush water, large quantities of ammonia are volatilized, causing even further elevated levels of ammonia gas inside and outside the rearing facility.
High atmospheric ammonia levels in swine rearing facilities have been shown to have a significant negative effect on feed consumption, feed conversion and daily weight gain in pigs. High levels of atmospheric ammonia in swine rearing facilities also increase the susceptibility of swine to micro-organisms responsible for respiratory problems, such as P. multocida. Ammonia also increases the susceptibility of four week old pigs to conchal atrophy. Likewise, high ammonia levels in swine facilities may play a significant role in the development of atrophic rhinitis. Similar problems are reported in poultry houses.
Another detrimental aspect of NH3 volatilization from poultry and hog manure is the effect on acid rain. The reportedly dominant source of atmospheric NH3 in Europe is livestock waste, with long term trends showing a 50% increase in NH3 emissions in Europe from 1950 to 1980. Ammonia raises the pH of rainwater, which allows more SO2 to dissolve in it. Ammonium sulfate then forms, which oxidizes in the soil, releasing nitric and sulfuric acid. This produces two to five times the acid input to soils previously described for acid atmospheric deposition, resulting in extremely low pH values (2.8–3.5) and high levels of dissolved aluminum in non-calcareous soils. Ammonia volatilization can also contribute to eutrophication. Reports show that nitrogen deposited via wet fallout tripled in Denmark from 1955 to 1980, corresponding to increases in nitrogen losses from agricultural operations during this period. The rising levels of nitrogen in the fallout have also been linked to the NH3 content in Danish streams.
Atmospheric ammonia can also result in the formation of ammonium nitrate particles in the air. These particles, which are usually less than 2 microns in size, contribute greatly to small airborne particles referred to as PM-10's (particulate matter less than 10 microns).
Poultry and swine (Sus scrofa domesticus) production is currently on the rise in the United States. As the poultry and swine industry moves into watersheds susceptible to eutrophication, various groups have voiced concern over water pollution. Modern poultry and swine rearing facilities often have large numbers of animals and a relatively limited land base to apply the manure. This leads to excessive application of nutrients, especially phosphorus, to the land. Phosphorus is considered to be the primary cause of eutrophication of freshwater systems. The threat of eutrophication due to phosphorus runoff has already resulted in limits being placed on the amount of animal units produced per area of land in The Netherlands.